Speech recognition with feeback from natural language processing for adaptation of acoustic model

ABSTRACT

A speech processing system including a speech recognition unit to receive input speech, and a natural language processor. The speech recognition unit performs speech recognition on input speech using acoustic models to produce a speech recognition result. The natural-language processor performs natural language processing on speech recognition result, and includes: a speech zone detector configured to detect correct zones from the speech recognition result; a feedback unit to feed back information obtained as a result of the natural language processing performed on the speech recognition result to said speech recognition unit. The feedback information includes the detected correct zones. The speech recognition unit includes an adaptation processor to process the feedback information to adapt the acoustic models so that the speech recognition unit produces the speech recognition result with higher precision than when the adaptation processor is not used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 09/676,644, entitled “SPEECH RECOGNITION WITH FEEDBACK FROMNATURAL LANGUAGE PROCESSING FOR ADAPTATION OF ACOUSTIC MODELS,” filedSep. 29, 2000. Benefit of priority of the filing date of Sep. 29, 2000is hereby claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to speech processing apparatuses, speechprocessing methods, and recording media for speech processing. Moreparticularly, the invention relates to a speech processing apparatus anda speech processing method for performing easy and highly preciseadaptation of models used for speech recognition. The invention alsorelates to a recording medium for storing a program implementing theabove-described method.

2. Description of the Related Art

One of the known speech recognition algorithms is the Hidden MarkovModel (HMM) method for recognizing input speech by using models. Morespecifically, in the HMM method, models (HMMs) defined by a transitionprobability (the probability of a transition from one state to anotherstate) and an output probability (the probability of a certain symbolbeing output upon the occurrence of the transition of the state) arepredetermined by learning, and then, the input speech is recognized byusing the models.

In performing speech recognition, on-line adaptation processing is knownin which the models are sequentially adapted by using the input speechin order to improve the recognition accuracy. According to this on-lineadaptation processing, the precision of acoustic models is progressivelyenhanced and the task of language models is progressively adaptedaccording to the amount of speech input by the speaker. Thus, thisprocessing is an effective means for improving the recognition accuracy.

Methods for adapting the models are largely divided into two types: onetype is “supervised learning” in which this method is implemented byproviding a correct answer from a supervisor, and the other type is“unsupervised learning” in which this method is implemented by providingdata which may be a correct answer (i.e., it is not certain that thedata is actually correct) from a supervisor.

One conventional “unsupervised learning” method is the one disclosed in,for example, Japanese Unexamined Patent Application Publication No.11-85184, in which adaptation of models is performed on input speech byusing the speech recognition result as a supervisor in a speechrecognition apparatus. In a conventional “unsupervised learning” method,such as the one disclosed in the above-described publication, it is notchecked with the user whether the speech recognition result is correct.Thus, in this method, there is less burden on the user, but on the otherhand, the reliability of the data used as a supervisor is not highenough, whereby the models may not be sufficiently adapted for thespeaker.

One conventional “supervised learning” method is the one discussed in,for example, Q. Huo et al., A study of on-line Quasi-Bayes adaptationfor DCHMM-based speech recognition, Proceedings of the InternationalConference on Acoustics, Speech and Signal Processing 1996, pp. 705-708.In a speech recognition apparatus, the user is requested to issue acertain amount of speech, and the models are adapted by using thespeech. Alternatively, in a speech recognition apparatus, the user isrequested to check whether the speech recognition result is correct, andthe models are adapted by using the result which was determined to becorrect.

However, the above-described model adaptation method implemented byrequiring a certain amount of speech is not suitable for on-lineadaptation. The model adaptation method performed on input speech byusing the speech recognition result as a supervisor in a speechrecognition apparatus. In a conventional “unsupervised learning” method,such as the one disclosed in the above-described publication, it is notchecked with the user whether the speech recognition result is correct.Thus, in this method, there is less burden on the user, but on the otherhand, the reliability of the data used as a supervisor is not highenough, whereby the models may not be sufficiently adapted for thespeaker.

One conventional “supervised learning” method is the one discussed in,for example, Q. Huo et al., A study of on-line Quasi-Bayes adaptationfor DCHMM-based speech recognition, Proceedings of the InternationalConference on Acoustics, Speech and Signal Processing 1996, pp. 705-708.In a speech recognition apparatus, the user is requested to issue acertain amount of speech, and the models are adapted by using thespeech. Alternatively, in a speech recognition apparatus, the user isrequested to check whether the speech recognition result is correct, andthe models are adapted by using the result which was determined to becorrect.

However, the above-described model adaptation method implemented byrequiring a certain amount of speech is not suitable for on-lineadaptation. The model adaptation method implemented by requesting theuser to check the speech recognition result imposes a heavy burden onthe user.

Another method for adapting models is the one disclosed in, for example,Japanese Unexamined Patent Application Publication No. 10-198395, inwhich language models or data for creating language models are preparedaccording to tasks, such as according to specific fields or topics, anddifferent tasks of language models are combined to create ahigh-precision task-adapted language model off-lines. In order toperform on-line adaptation by employing this method, however, it isnecessary to infer the type of task of the speech, which makes itdifficult to perform adaptation by the single use of a speechrecognition apparatus.

SUMMARY OF THE INVENTION

Accordingly, in view of the above background, it is an object of thepresent invention to achieve high-precision adaptation of models usedfor speech recognition without imposing a burden on a user.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a speech processing apparatusincluding a speech recognition unit for performing speech recognition,and a natural-language processing unit for performing natural languageprocessing on a speech recognition result obtained from the speechrecognition unit. The natural-language processing unit includes afeedback device for feeding back information obtained as a result of thenatural language processing performed on the speech recognition resultto the speech recognition unit. The speech recognition unit includes aprocessor for performing processing based on the information fed backfrom the feedback device.

The speech recognition unit may perform speech recognition by usingmodels, and the processor may perform adaptation of the models based onthe information fed back from the feedback device.

The feedback device may feed back at least one of speech recognitionresult zones which are to be used for the adaptation of the models andspeech recognition result zones which are not to be used for theadaptation of the models. Alternatively, the feedback device may feedback the speech recognition result which appears to be correct. Or, thefeedback device may feed back the reliability of the speech recognitionresult. Alternatively, the feedback device may feed back a task of thespeech recognition result.

The feedback device may feed back at least one of speech recognitionresult zones which are to be used for the adaptation of the models,speech recognition result zones which are not to be used for theadaptation of the models, the speech recognition result which appears tobe correct, the reliability of the speech recognition result, and a taskof the speech recognition result.

According to another aspect of the present invention, there is provideda speech processing method including a speech recognition step ofperforming speech recognition, and a natural-language processing step ofperforming natural language processing on a speech recognition resultobtained in the speech recognition step. The natural-language processingstep includes a feedback step of feeding back information obtained as aresult of the natural language processing performed on the speechrecognition result to the speech recognition step. The speechrecognition step includes a process step of performing processing basedon the information fed back from the feedback step.

According to still another aspect of the present invention, there isprovided a recording medium for recording a program which causes acomputer to perform speech recognition processing. The program includesa speech recognition step of performing speech recognition, and anatural-language processing step of performing natural languageprocessing on a speech recognition result obtained in the speechrecognition step. The natural-language processing step includes afeedback step of feeding back information obtained as a result of thenatural language processing performed on the speech recognition resultto the speech recognition step. The speech recognition step includes aprocess step of performing processing based on the information fed backfrom the feedback step.

Thus, according to the speech processing apparatus, the speechprocessing method, and the recording medium of the present invention,information obtained as a result of natural language processingperformed on a speech recognition result is fed back, and processing isperformed based on the fed back information. It is thus possible toperform adaptation of the models used for speech recognition with highprecision without imposing a burden on the user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of the configurationof a speech processing system incorporating the present invention;

FIG. 2 illustrates an overview of the operation performed by the speechprocessing system shown in FIG. 1;

FIG. 3 is a block diagram illustrating a first example of theconfiguration of a speech recognition unit 1;

FIG. 4 is a block diagram illustrating a first example of theconfiguration of a machine translation unit 2;

FIG. 5 is a block diagram illustrating an example of the configurationof a speech synthesizing unit 3;

FIG. 6 is a block diagram illustrating a first example of theconfiguration of a dialog management unit 5;

FIG. 7 is a flow chart illustrating a first example of the operation ofthe speech processing system;

FIG. 8 is a block diagram illustrating a second example of theconfiguration of the dialog management unit 5;

FIG. 9 is a flow chart illustrating a second example of the operation ofthe speech processing system;

FIG. 10 is a block diagram illustrating a third example of theconfiguration of the dialog management unit 5;

FIG. 11 is a flow chart illustrating a third example of the operation ofthe speech processing system;

FIG. 12 is a block diagram illustrating a fourth example of theconfiguration of the dialog management unit 5;

FIG. 13 is a flow chart illustrating a fourth example of the operationof the speech processing system;

FIG. 14 is a block diagram illustrating a second example of theconfiguration of the speech recognition unit 1;

FIG. 15 is a block diagram illustrating a second example of theconfiguration of the machine translation unit 2;

FIG. 16 is a flow chart illustrating a fifth example of the operation ofthe speech processing system;

FIG. 17 is a flow chart illustrating the operation of the speechrecognition unit 1 shown in FIG. 14;

FIG. 18 is a flow chart illustrating the operation of the machinetranslation unit 2 shown in FIG. 15;

FIG. 19 is a block diagram illustrating a third example of theconfiguration of the speech recognition unit 1;

FIG. 20 is a block diagram illustrating a third example of theconfiguration of the machine translation unit 2;

FIG. 21 is a block diagram illustrating an example of the configurationof a language converter 22 shown in FIG. 20;

FIG. 22 illustrates an example of a thesaurus;

FIG. 23 is a flow chart illustrating a first example of the operation ofthe machine translation unit 2 shown in FIG. 20;

FIG. 24 is a flow chart illustrating template selection processingperformed in a matching portion 51;

FIG. 25 illustrates the accents of three Japanese words;

FIG. 26 is a flow chart illustrating a second example of the operationof the machine translation unit 2 shown in FIG. 20;

FIG. 27 is a block diagram illustrating a fourth example of theconfiguration of the speech recognition unit 1;

FIG. 28 is a block diagram illustrating a fourth example of theconfiguration of the machine translation unit 2;

FIG. 29 is a flow chart illustrating the operation of the machinetranslation unit 2 shown in FIG. 28;

FIGS. 30A, 30B, and 30C illustrate recording media according to thepresent invention; and

FIG. 31 is a block diagram illustrating an example of the configurationof a computer 101 shown in FIG. 30.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is discussed more fully below with reference tothe accompanying drawings through illustration of a preferredembodiment.

FIG. 1 illustrates the configuration of a speech processing system(system designates a logical collection of a plurality of apparatuses,and it is not essential that the individual apparatuses be within thesame casing) incorporating the present invention.

In this speech processing system, speech is input, and a reply is outputaccordingly. A translation of the speech is also output. Additionally, areply may also be translated into a language other than the languageused for the input speech, and the translated reply is then output.

More specifically, speech, such as Japanese speech, is input, into aspeech recognition unit 1. The speech recognition unit 1 then recognizesthe input speech, and outputs text and other associated information to amachine translation unit 2, a display unit 4, a dialog management unit5, etc. as a speech recognition result.

The machine translation unit 2 analyzes the speech recognition resultoutput from the speech recognition unit 1 so as to machine-translate theinput speech into a language other than the language used for the inputspeech, for example, into English, and outputs text and associatedinformation to a speech synthesizing unit 3, the display unit 4, thedialog management unit 5, and so on, as a translation result. The speechsynthesizing unit 3 then performs speech synthesis based on the outputsof the machine translation unit 2 and the dialog management unit 5, andthen outputs the synthesized speech as a reply to the input speech or asa translation result of the input speech.

The display unit 4, which is formed of, for example, a liquid crystaldisplay, displays the speech recognition result obtained from the speechrecognition unit 1, the machine translation result obtained from themachine translation unit 2, the reply created by the dialog managementunit 5, etc.

The dialog management unit 5 creates a reply to the speech recognitionresult obtained from the speech recognition unit 1, and outputs it tothe machine translation unit 2, the speech synthesizing unit 3, thedisplay unit 4, the dialog management unit 5, and so on. The dialogmanagement unit 5 also forms a reply to the machine translation resultobtained from the machine translation unit 2, and outputs it to thespeech synthesizing unit 3 and the display unit 4.

In the above-configured speech processing system, to output a reply toinput speech, the input speech is first recognized in the speechrecognition unit 1, and is output to the dialog management unit 5. Thedialog management unit 5 forms a reply to the speech recognition resultand supplies it to the speech synthesizing unit 3. The speechsynthesizing unit 3 then creates a synthesized speech corresponding tothe reply formed by the dialog management unit 5.

In outputting a translation of the input speech, the input speech isfirst recognized in the speech recognition unit 1, and is supplied tothe machine translation unit 2. The machine translation unit 2machine-translates the speech recognition result and supplies it to thespeech synthesizing unit 3. The speech synthesizing unit 3 then createsa synthesized speech in response to the translation result obtained fromthe machine translation unit 2 and outputs it.

In translating a reply to the input speech into another language andoutputting it, the input speech is first recognized in the speechrecognition unit 1 and is output to the dialog management unit 5. Thedialog management unit 5 then forms a reply to the speech recognitionresult from the speech recognition unit 1, and supplies it to themachine translation unit 2. The machine translation unit 2 thenmachine-translates the reply and supplies it to the speech synthesizingunit 3. The speech synthesizing unit 3 forms a synthesized speech inresponse to the translation result from the machine translation unit 2and outputs it.

In the above-described case, namely, in translating a reply to the inputspeech into another language and outputting it, the speech recognitionresult from the speech recognition unit 1 may first bemachine-translated in the machine translation unit 2, and then, a replyto the translation result may be created in the dialog management unit5. Subsequently, a synthesized speech corresponding to the reply may beformed in the speech synthesizing unit 3 and output.

In the speech processing system shown in FIG. 1, a user's speech (inputspeech) is recognized in the speech recognition unit 1, as shown in FIG.2, and the speech recognition result is processed in the machinetranslation unit 2 and the dialog management unit 5, which togetherserve as a natural-language processing unit for performing naturallanguage processing, such as machine translation and dialog management.In this case, the machine translation unit 2 and the dialog managementunit 5 feed back to the speech recognition unit 1 the informationobtained as a result of the natural language processing performed on thespeech recognition result. The speech recognition unit 1 then executesvarious types of processing based on the information which is fed backas discussed above (hereinafter sometimes referred to as “feedbackinformation”).

More specifically, the machine translation unit 2 and the dialogmanagement unit 5 feed back useful information for adapting models usedin the speech recognition unit 1, and the speech recognition unit 1performs model adaptation based on the useful information. Also, forfacilitating the execution of the natural language processing on thespeech recognition result by the speech recognition unit 1, the machinetranslation unit 2 and the dialog management unit 5 feed back, forexample, information for altering the units of speech recognitionresults, and the speech recognition unit 1 then alters the unit ofspeech based on the above information. Additionally, the machinetranslation unit 2 and the dialog management unit 5 feed back, forexample, information for correcting errors of the speech recognitionresult made by the speech recognition unit 1, and the speech recognitionunit 1 performs suitable processing for obtaining a correct speechrecognition result.

FIG. 3 illustrates a first example of the configuration of the speechrecognition unit 1 shown in FIG. 1.

Speech from the user is input into a microphone 11 in which the speechis converted into an audio signal as an electric signal. The audiosignal is then supplied to an analog-to-digital (AD) converter 12. Aftersampling and quantizing the analog audio signal from the microphone 11,the AD converter 12 converts it into a digital audio signal. The digitalaudio signal is then supplied to a feature extracting portion 13.

The feature extracting portion 13 extracts, from the audio data from theAD converter 12, feature parameters, for example, the spectrum, linearprediction coefficient, cepstrum coefficient, and line spectrum pair, ofeach frame, and supplies them to a feature buffer 14 and a matchingportion 15. The feature buffer 14 temporarily stores the featureparameters supplied from the feature extracting portion 13.

The matching portion 15 recognizes the speech input into the microphone11, based on the feature parameters from the feature extracting portion13 and the feature parameters stored in the feature buffer 14, whilereferring to an acoustic model database 16, a dictionary database 17,and a grammar database 18 as required.

More specifically, the acoustic model database 16 stores acoustic modelsrepresenting the acoustic features, such as the individual phonemes andsyllables, of the language corresponding to the speech to be recognized.As the acoustic models, HMM models may be used. The dictionary database17 stores a word dictionary indicating the pronunciation models of thewords to be recognized. The grammar database 18 stores grammar rulesrepresenting the collocation (concatenation) of the individual wordsregistered in the word dictionary of the dictionary database 17. Thegrammar rules may include rules based on the context-free grammar (CFG)and the statistical word concatenation probability (N-gram).

The matching portion 15 connects acoustic models stored in the acousticmodel database 16 by referring to the word dictionary of the dictionarydatabase 17, thereby forming the acoustic models (word models) of thewords. The matching portion 15 then connects some word models byreferring to the grammar rules stored in the grammar database 18, and byusing such connected word models, recognizes the speech input into themicrophone 11 based on the feature parameters according to, for example,the HMM method.

Then, the speech recognition result obtained by the matching portion 15is output in, for example, text format.

Meanwhile, an adaptation processor 19 receives the speech recognitionresult from the matching portion 15. Upon receiving the above-describedfeedback information, which is discussed more fully below, from thedialog management unit 5, the adaptation processor 19 extracts, from thespeech recognition result, models suitable for adapting the acousticmodels in the acoustic model database 16 and the language models in thedictionary database 17 based on the feedback information. By using thespeech recognition result as a supervisor for performing preciseadaptation, on-line adaptation is performed on the acoustic models inthe acoustic model database 16 and the language models in the dictionarydatabase 17 (hereinafter both models are simply referred to as“models”).

It is now assumed that the HMMs are used as the acoustic models. In thiscase, the adaptation processor 19 performs model adaptation by alteringthe parameters, such as the average value and the variance, which definethe transition probability or the output probability representing theHMM, by the use of the speech recognition result.

FIG. 4 illustrates a first example of the configuration of the machinetranslation unit 2 shown in FIG. 1.

Text as the speech recognition result output from the speech recognitionunit 1 and text as a reply output from the dialog management unit 5 areinput into a text analyzer 21. The text analyzer 21 then analyzes thetext while referring to a dictionary database 24 and an analyzinggrammar database 25.

More specifically, the dictionary database 24 stores a word dictionarydesignating the notation of the individual words, the word-classinformation, etc., required for the application of the analyzinggrammar. The analyzing grammar database 25 stores analyzing grammarrules designating the restrictions concerning the word concatenation,etc. based on the information on the individual words of the worddictionary. The text analyzer 21 conducts morpheme analyses and syntaxanalyses on the input text based on the word dictionary and theanalyzing grammar rules, thereby extracting language information of, forexample, words and syntax, forming the input text. The analyzingtechniques employed by the text analyzer 21 may include techniques usingregular grammar, the context-free grammar (CFG), and the statisticalword concatenation probability.

The language information obtained in the text analyzer 21 as an analysisresult of the input text is supplied to a language converter 22. Thelanguage converter 22 converts the language information of the inputtext into that of a translated language by referring to a languageconversion database 26.

That is, the language conversion database 26 stores language conversiondata, such as conversion patterns (templates) from language informationof an input language (i.e., the language input into the languageconverter 22) into that of an output language (i.e., the language outputfrom the language converter 22), examples of translations between aninput language and an output language, and thesauruses used forcalculating the similarities between the input language and thetranslation examples. Based on such language conversion data, thelanguage converter 22 converts the language information of the inputtext into that of an output language.

The language information of the output language acquired in the languageconverter 22 is supplied to a text generator 23. The text generator 23then forms text of the translated output language based on thecorresponding language information by referring to a dictionary database27 and a text-forming grammar database 28.

That is, the dictionary database 27 stores a word dictionary describingthe word classes and the word inflections required for forming outputlanguage sentences. The text-forming grammar database 28 storesinflection rules of the required words and text-forming grammar rules,such as restrictions concerning the word order. Then, the text generator23 converts the language information from the language converter 22 intotext based on the word dictionary and the text-forming grammar rules,and outputs it.

FIG. 5 illustrates an example of the configuration of the speechsynthesizing unit 3 shown in FIG. 1.

Text as a translation result output from the machine translation unit 2and text as a reply output from the dialog management unit 5 are inputinto a text analyzer 31. The text analyzer 31 analyzes the input textwhile referring to a dictionary database 34 and an analyzing grammardatabase 35.

More specifically, the dictionary database 34 stores a word dictionarydescribing the word class information and the phonetic and accentinformation of the individual words. The analyzing grammar database 35stores analyzing grammar rules, such as restrictions on the wordconcatenation, concerning the words entered in the word dictionary ofthe dictionary database 34. The text analyzer 31 then conducts morphemeanalyses and syntax analyses on the input text based on the worddictionary and the analyzing grammar rules so as to extract informationrequired for ruled speech-synthesizing, which is to be performed in aruled speech synthesizer 32. The information required for ruledspeech-synthesizing may include information for controlling thepositions of pauses, the accent and intonation, prosodic information,and phonemic information, such as the pronunciation of the words.

The information obtained from the text analyzer 31 is supplied to theruled speech synthesizer 32. The ruled speech synthesizer 32 generatesaudio data (digital data) of a synthesized speech corresponding to thetext input into the text analyzer 31 by referring to a phoneme database36.

The phoneme database 36 stores phoneme data in the form of, for example,CV (Consonant, Vowel), VCV, or CVC. The ruled speech synthesizer 32connects required phoneme data based on the information from the textanalyzer 31, and also appends pauses, accents, and intonation, asrequired, to the connected phonemes, thereby generating audio data of asynthesized speech corresponding to the text input into the textanalyzer 31.

The audio data is then supplied to a DA converter 33 in which it isconverted into an analog audio signal. The analog audio signal is thensupplied to a speaker (not shown), so that the corresponding synthesizedspeech is output from the speaker.

FIG. 6 illustrates a first example of the configuration of the dialogmanagement unit 5 shown in FIG. 1.

The speech recognition result obtained from the speech recognition unit1 is supplied to a dialog processor 41 and a speech zone detector 42.The dialog processor 41 creates a reply to the speech recognition resultand outputs it. Meanwhile, the speech zone detector 42 monitors a replyto be output from the dialog processor 41. Based on this reply, thespeech zone detector 42 detects the zones to be used for adapting themodels (hereinafter sometimes referred to as “adaptation zones”) fromthe speech recognition result, and feeds back the adaptation zones tothe adaptation processor 19 of the speech recognition unit 1 as thefeedback information.

Alternatively, speech recognition zones which are not to be used foradapting the models may be fed back to the speech recognition unit 1 asthe feedback information. Or, both the speech recognition zones whichare to be used for model adaptation and those which are not to be usedtherefor may be fed back.

A description is now given, with reference to the flow chart of FIG. 7,of the operation of the speech processing system which is provided withthe speech recognition unit 1 such as the one shown in FIG. 3 and thedialog management unit 5 such as the one shown in FIG. 6.

The user issues speech and the corresponding speech is input into thespeech recognition unit 1. Then, in step S1, the speech recognition unit1 recognizes the input speech and outputs the resulting text to, forexample, the dialog management unit 5 as the speech recognition result.

In step S2, the dialog processor 41 of the dialog management unit 5creates a reply to the speech recognition result output from the speechrecognition unit 1 and outputs the reply. Subsequently, in step S3, thespeech zone detector 42 determines from the reply from the dialogprocessor 41 whether the speech recognition result is correct. If theoutcome of step S3 is no, steps S4 and S5 are skipped, and theprocessing is completed.

On the other hand, if it is determined in step S3 that the speechrecognition result is correct, the process proceeds to step S4 in whichthe speech zone detector 42 detects correct zones from the speechrecognition result, and transmits them to the adaptation processor 19 ofthe speech recognition unit 1 (FIG. 3) as adaptation zones.

Then, in step S5, in the adaptation processor 19, by using only theadaptation zones output from the speech zone detector 42 among thespeech recognition result output from the matching portion 15,adaptation of the models is conducted, and the processing is thencompleted.

According to the aforementioned processing, the models used for speechrecognition can be precisely adapted without imposing a burden on theuser.

More specifically, it is now assumed, for example, that the followingdialog concerning the purchase of a concert ticket may be made betweenthe speech processing system shown in FIG. 1 and the user.User: “Hello. I'd like to have one ticket for the Berlin PhilharmonicOrchestra on September 11.”  (1)Reply: “One ticket for the Berlin Philharmonic Orchestra on September11? Tickets are available for S to D seats. Which one would youlike?”  (2)User: “S, please.”  (3)Reply: “A?”  (4)User: “No, S.”  (5)Reply: “S. We will reserve the 24th seat on the fourth row downstairs.The price is 28,000 yen. Is that all right?”  (6)User: “Fine.”  (7)Reply: “Thank you.”  (8)

In the dialog from (1) to (8), the speech zone detector 42 determinesthe speech recognition results of user's speech (1), (5), and (7) to becorrect from the associated replies (2), (6), and (8), respectively.However, the speech recognition result of user's speech (3) isdetermined to be wrong since the user re-issues speech (5) to reply (4)which is made in response to speech (3).

In this case, the speech zone detector 42 feeds back the correct zonesof the speech recognition results corresponding to user's speech (1),(5), and (7) to the adaptation processor 19 as the feedback information(the zone of the speech recognition result corresponding to user'sspeech (3) which was determined to be wrong is not fed back). As aresult, by using only the above-mentioned speech recognition correctzones, i.e., by employing the correct speech recognition result as asupervisor and by using the user's speech corresponding to the correctspeech recognition result as a learner, adaptation of the models isperformed.

Accordingly, by the use of only correct recognition results, it ispossible to achieve highly precise adaptation of the models (resultingin a higher recognition accuracy). Additionally, a burden is not imposedon the user.

FIG. 8 illustrates a second example of the configuration of the dialogmanagement unit 5 shown in FIG. 1. The same elements as those shown inFIG. 6 are designated with like reference numerals. The dialogmanagement unit 5 shown in FIG. 8 is configured similarly to thecounterpart shown in FIG. 6, except that a correcting portion 43 isprovided instead of the speech zone detector 42.

The correcting portion 43 monitors replies output from the dialogprocessor 41 and determines based on the replies whether the speechrecognition results output from the speech recognition unit 1 arecorrect, and if so, the correcting portion 43 feeds back the speechrecognition results to the adaptation processor 19 as the feedbackinformation. If the speech recognition results are found to be wrong,the correcting portion 43 corrects (or modifies) the results and feedsthem back to the adaptation processor 19 as the feedback information.

A description is now given, with reference to the flow chart of FIG. 9,of the operation of the speech processing system shown in FIG. 1 whichis provided with the speech recognition unit such as the one shown inFIG. 3 and the dialog management unit 5 such as the one shown in FIG. 8.In steps S11 and S12, processes similar to those of steps S1 and S2,respectively, of FIG. 7 are executed. Then, a reply to the speechrecognition result from the speech recognition unit 1 is output from thedialog processor 41.

The process then proceeds to step S13 in which the correcting portion 43determines from the reply from the dialog processor 41 whether thespeech recognition result is correct. If the outcome of step S13 is yes,the process proceeds to step S14. In step S14, the correcting portion 43transmits the correct speech recognition result to the adaptationprocessor 19 of the speech recognition unit 1 as the feedbackinformation.

In step S15, the adaptation processor 19 performs adaptation of themodels by using the correct speech recognition result from thecorrecting portion 43 as the feedback information. The processing isthen completed.

On the other hand, if it is found in step S13 that the speechrecognition result from the speech recognition unit is wrong, the flowproceeds to step S16. In step S16, the correcting portion 43 corrects(modifies) the speech recognition result based on the reply from thedialog processor 41, and sends the corrected (modified) result to theadaptation processor 19 as the feedback information.

In step S15, the adaptation processor 19 conducts adaptation of themodels by using the corrected (modified) speech recognition result fromthe correcting portion 43. The processing is then completed.

According to the above-described processing, as well as the previousprocessing, models used for speech recognition can be adapted with highprecision without burdening the user.

It is now assumed, for example, that the aforementioned dialog from (1)to (8) is made between the speech processing system shown in FIG. 1 andthe user. Then, the correcting portion 43 determines that the speechrecognition results of user's speech (1), (5), and (7) are correct fromthe associated replies (2), (6), and (8), respectively. In contrast, thecorrecting portion 43 determines that the speech recognition result ofuser's speech (3) is wrong since the user re-issues speech (5) inresponse to reply (4).

In this case, the correcting portion 43 feeds back the correct speechrecognition results of user's speech (1), (5), and (7) to the adaptationprocessor 19 as the feedback information. The adaptation processor 19then performs adaptation of the models by using the correct speechrecognition results and the associated user's speech (1), (5), and (7).

The correcting portion 43 also corrects for the wrong speech recognitionresult of user's speech (3) based on the correct recognition result ofuser's subsequent speech (5). More specifically, the correcting portion43 makes the following analyses on reply “A?” (4) to user's speech “S,please.” (3): “S” has been wrongly recognized as “A” in (3) since user'ssubsequent speech (5) “No, S.” has been correctly recognized, and thus,the correct recognition result should be “S” in user's speech (3).Accordingly, as a result of the above-described analyses, the correctingportion 43 corrects the speech recognition result which was wronglyrecognized as “A” rather than “S”, and feeds back the corrected resultto the adaptation processor 19 as the feedback information. In thiscase, the adaptation processor 19 performs adaptation of the models byusing the corrected speech recognition result and the correspondinguser's speech (3).

Thus, even if speech is wrongly recognized, a wrong recognition resultcan be corrected (modified), and adaptation of the models is performedbased on the corrected (modified) result. As a consequence, models canbe precisely adapted without burdening the user, resulting in a higherrecognition accuracy.

FIG. 10 illustrates a third example of the configuration of the dialogmanagement unit 5 shown in FIG. 1. The same elements as those shown inFIG. 6 are designated with like reference numerals. That is, the dialogmanagement unit 5 shown in FIG. 10 is configured similarly to that shownin FIG. 6, except that the speech zone detector 42 is substituted with areliability calculator 44.

The reliability calculator 44 monitors replies output from the dialogprocessor 41. Based on the replies, the reliability calculator 44calculates the reliability of the speech recognition result output fromthe speech recognition unit 1, and feeds back the calculated reliabilityto the adaptation processor 19 as the feedback information.

A description is now given, with reference to the flow chart of FIG. 11,of the operation of the speech processing system shown in FIG. 1 whichis provided with the speech recognition unit 1 such as the one shown inFIG. 3 and the dialog management unit 5 such as the one shown in FIG.10.

In steps S21 and S22, the processes similar to those of steps S1 and S2,respectively, of FIG. 7 are executed. Then, a reply to the speechrecognition result from the speech recognition unit 1 is output from thedialog processor 41.

Subsequently, in step S23, the reliability calculator 44 sets, forexample, the number 0 or 1, as the reliability of the speech recognitionresult from the reply output from the dialog processor 41. Then, in stepS24, the reliability calculator 44 transmits the calculated reliabilityto the adaptation processor 19 as the feedback information.

Then, in step S25, the adaptation processor 19 carries out adaptation ofthe models by using the reliability from the reliability calculator 44as the feedback information. The processing is then completed.

According to the foregoing processing, models used for speechrecognition can be adapted with high precision without imposing a burdenon the user.

More specifically, it is now assumed, for example, that theaforementioned dialog from (1) to (8) is made between the speechprocessing system shown in FIG. 1 and the user. Then, the reliabilitycalculator 44 determines that the speech recognition results of user'sspeech (1), (5), and (7) are correct from the corresponding replies (2),(6), and (8), respectively. On the other hand, the speech recognitionresult of user's speech (3) is determined to be wrong since the userre-issues speech (5) in response to the corresponding reply (4).

In this case, the reliability calculator 44 sets the reliabilities ofthe correct speech recognition results of user's speech (1), (5), and(7) to 1, and sets the reliability of the wrong speech recognitionresult of user's speech (3) to 0, and feeds back the calculatedreliabilities to the adaptation processor 19. Then, the adaptationprocessor 19 performs adaptation of the models by employing user'sspeech (1), (3), (5), and (7) and the associated speech recognitionresults with weights according to the corresponding reliabilities.

The adaptation of models is thus conducted by using only the correctspeech recognition results. It is thus possible to accomplish highlyprecise adaptation of the models without burdening the user.

As the reliability, intermediate values between 0 and 1 may be used, inwhich case, they can be calculated by using the likelihood of the speechrecognition result from the speech recognition unit 1. In this case,adaptation of the models may be performed by using such reliabilities,for example, according to the following equation:P _(new)=(1−(1−α)×R)×P _(old)+(1−α)×R×P _(adapt)where P_(new) represents the parameter of the adapted model (as statedabove, which is the average value or the variance defining thetransition probability or the output probability if the models areHMMs); ( indicates a predetermined constant for making adaptation; Rdesignates the reliability; P_(old) represents the parameter of thepre-adapted model; and P_(adapt) indicates data used for adaptation,obtained from the user's speech.

FIG. 12 illustrates a fourth example of the dialog management unit 5shown in FIG. 1. The same elements as those shown in FIG. 6 areindicated by like reference numerals. The dialog management unit 5 shownin FIG. 12 is configured similarly to the counterpart shown in FIG. 6,except that a task inference portion 45 is provided instead of thespeech zone detector 42.

By monitoring the replies output from the dialog processor 41, the taskinference portion 45 infers, based on the reply, the type of taskcorresponding to the speech recognition result output from the speechrecognition unit 1 and feeds back the task to the adaptation processor19 as the feedback information.

A description is now given, with reference to the flow chart of FIG. 13,of the operation of the speech processing system shown in FIG. 1provided with the speech recognition unit 1 such as the one shown inFIG. 1 and the dialog management unit 5 such as the one shown in FIG.12. In this speech processing system, the dictionary database 17 of thespeech recognition unit 1 stores dictionaries according to tasks, suchas language models for reservations of concert tickets, language modelsfor hotel reservations, language models for reservations of airlinetickets, language models for dictations, such as newspaper reading, andother types of language models.

In steps S31 and S32, processes similar to those of steps S1 and S2,respectively, of FIG. 7 are executed. Then, a reply to the speechrecognition result from the speech recognition unit 1 is output from thedialog processor 41.

In step S33, the task inference portion 45 infers the task (field ortopic) associated with the speech recognition result from the speechrecognition unit 1 from the reply output from the dialog processor 41.Then, in step S34, the task inference portion 45 sends the task to theadaptation processor 19 of the speech recognition unit 1 as the feedbackinformation.

In step S35, the adaptation processor 19 performs adaptation of themodels by using the task from the task inference portion 45 as thefeedback information. The processing is then completed.

More specifically, it is now assumed that the aforementioned dialog from(1) to (8) is made between the speech processing system shown in FIG. 1and the user. The task inference portion 45 infers from the speechrecognition results of the user's speech and the associated replies thatthe task is concerned with a reservation for a concert ticket, and thenfeeds back the task to the adaptation processor 19. In this case, in theadaptation processor 19, among the language models sorted according totask in the dictionary database 17, only the language models for concertticket reservations undergo adaptation.

It is thus possible to achieve highly precise adaptation of the modelsused for speech recognition without imposing a burden on the user.

In the dictionary database 17, data used for creating language modelsmay be stored according to tasks rather than the language modelsthemselves, in which case, the adaptation may be performed accordingly.

Although in the above-described example the language models sortedaccording to task are adapted, acoustic models sorted according to taskmay be adapted.

More specifically, to improve the recognition accuracy for numericcharacters, acoustic models for numeric characters (hereinaftersometimes referred to as “numeric character models”) are sometimesprepared separately from acoustic models for items other than numericcharacters (hereinafter sometimes referred to as “regular acousticmodels”). Details of speech recognition performed by distinguishing thenumeric character models from the regular acoustic models are discussedin, for example, IEICE Research Report SP98-69, by Tsuneo KAWAI, KDDResearch Lab.

When both the numeric character models and the regular acoustic modelsare prepared, the task inference portion 45 infers whether the task ofthe speech recognition result is concerned with numeric characters, andby using the inference result, the numeric character models and theregular acoustic models are adapted in the adaptation processor 19.

More specifically, it is now assumed, for example, that theabove-described dialog (1) to (8) is made between the speech processingsystem shown in FIG. 1 and the user. Then, the task inference portion 45infers from the speech recognition result of the user's speech and theassociated reply that “9” and “1” in the speech recognition result ofuser's speech (1) “Hello. I'd like to have one ticket for the BerlinPhilharmonic Orchestra on September 11.” are a task of numericcharacters, and feeds back such a task to the adaptation processor 19.In this case, in the adaptation processor 19, the numeric charactersmodels are adapted by using the elements, such as “9” and “1”, of theuser's speech and the corresponding speech recognition result, while theregular acoustic models are adapted by using the other elements.

The adaptation of models may be performed by a combination of two ormore of the four adaptation methods described with reference to FIGS. 6through 13.

If the speech recognition result has been translated, theabove-described feedback information is output from the machinetranslation unit 2 to the speech recognition unit 1.

FIG. 14 illustrates a second example of the configuration of the speechrecognition unit 1 shown in FIG. 1. The same elements as those shown inFIG. 3 are designated with like reference numerals. That is, the speechrecognition unit 1 shown in FIG. 14 is basically configured similarly tothe counterpart shown in FIG. 3, except that the adaptation processor 19is not provided.

In the speech recognition unit 1 shown in FIG. 14, the matching portion15 is adapted to receive an alteration signal, which will be discussedin detail, from the machine translation unit 2 as the feedbackinformation. Upon receiving the alteration signal, the matching portion15 alters the unit which forms a speech recognition result (hereinaftersometimes referred to as “forming unit”).

More specifically, it is now assumed that a speech recognition result“kore wa nan desu ka?” (which means “What is this?”) is obtained inresponse to input speech “kore wa nan desu ka?”. In this case, uponreceiving the alteration signal, the matching portion 15 alters theforming unit of the speech recognition result from one unit, i.e., “korewa nan desu ka?” into three units, i.e., “korewa”, “nandesu”, and “ka”,or into five units, i.e., “kore”, “wa”, “nan”, “desu”, and “ka”, beforeoutputting the recognition result.

Such an alteration may be made by disconnecting the words or phrasesforming the initially obtained speech recognition result “kore wa nandesu ka?”, or by altering the unit of speech recognition processing(hereinafter sometimes referred to as “processing unit”) executed by thematching portion 15.

In the second case, the information for altering the processing unit maybe stored in the word dictionary in the dictionary database 17 or in thegrammar rules in the grammar database 18.

More specifically, for example, the phrase “korewa” is stored in theword dictionary in correspondence with words (morphemes) “kore” and “wa”forming such a phrase. Accordingly, by referring to the word dictionary,the matching portion 15 may obtain the speech recognition result formingone unit “korewa” or the speech recognition result forming two units“kore” and “wa” in response to the input speech “korewa”.

Although in the above-described example phrases are associated with thecorresponding words (morphemes), sentences may be associated with thecorresponding phrases, or with the corresponding phrases and words.

Alternatively, if the grammar rules in the grammar database 18 are usedfor altering the unit of speech recognition processing executed by thematching portion 15, certain rules may be stored in the grammar rules inthe grammar database 18. For example, the rule that the subject isformed by connecting the pronoun “kore” and the particle “wa” may bestored in the grammar rules. In this case, as well as in the previouscase, by referring to the grammar rules, in response to the input speech“korewa” which represents the subject formed by the pronoun “kore” andthe particle “wa”, the matching portion 15 obtains the speechrecognition result forming one unit, i.e., “korewa” or the speechrecognition result forming two units, i.e., “kore” and “wa”.

The aforementioned alteration of the processing unit may be made byusing one or both of the word dictionary and the grammar rules.Moreover, a plurality of word dictionaries may be prepared, andcorresponding grammar rules may be prepared accordingly. In this case,upon receiving an alteration signal, a combination of the required worddictionary and grammar rules may be selected.

If it becomes necessary to alter the forming unit by the alteration ofthe processing unit, the matching portion 15 re-processes the speechrecognition result by using feature parameters stored in the featurebuffer 14.

FIG. 15 illustrates a second example of the configuration of the machinetranslation unit 2 when the speech recognition unit 1 is constructedsuch as the one shown in FIG. 14. The same elements as those shown inFIG. 4 are indicated by like reference numerals. Basically, the machinetranslation unit 2 shown in FIG. 15 is configured similarly to thecounterpart shown in FIG. 4.

In the machine translation unit 2 in FIG. 15, the text analyzer 21determines whether the forming unit of input text is appropriate foranalyzing the text, and if so, analyzes the input text, as discussedabove. Conversely, if the forming unit of the input text is notappropriate for analyzing the text, the text analyzer 21 sends analteration signal to instruct an alteration of the forming unit to thespeech recognition unit 1 as the feedback information. As stated above,the speech recognition unit 1 alters the forming unit of the speechrecognition result based on the alteration signal. As a result, thespeech recognition result with the altered forming unit is supplied tothe text analyzer 21 as the input text. Then, the text analyzer 21re-determines whether the forming unit is appropriate for analyzing thetext. Thereafter, processing similar to the one described above isrepeated.

As in the case of the machine translation unit 2, the dialog managementunit 5 performs dialog management processing, which is one type ofnatural language processing, on the speech recognition result obtainedfrom the speech recognition unit 1. In this case, the dialog managementunit 5 may send an alteration signal to the speech recognition unit 1 ifrequired.

A description is given below, with reference to the flow chart of FIG.16, of the operation of the speech processing system (translationoperation) shown in FIG. 1 when the speech recognition unit 1 and themachine translation unit 2 are configured, as those shown in FIGS. 14and 15, respectively.

Upon receiving input speech, in step S41, the speech recognition unit 1recognizes the speech and outputs text to the machine translation unit 2as the speech recognition result. The process then proceeds to step S42.

In step S42, the machine translation unit 2 machine-translates the textfrom the speech recognition unit 1. Then, it is determined in step S43whether an alteration signal has been received in the speech recognitionunit 1 from the machine translation unit 2 as the feedback information.

If the outcome of step S43 is yes, the process returns to step S41 inwhich the speech recognition unit 1 changes the forming unit of thespeech recognition result in response to the alteration signal, andthen, re-performs the speech recognition processing and outputs the newspeech recognition result to the machine translation unit 2. Thereafter,processing similar to the one described above is repeated.

If it is found in step S43 that an alteration signal has not beenreceived from the machine translation unit 2 as the feedbackinformation, the machine translation unit 2 outputs the text obtained asa result of the translation processing in step S42 to the speechsynthesizing unit 3, and the process proceeds to step S44.

In step S44, the speech synthesizing unit 3 composes a synthesizedspeech corresponding to the text output from the machine translationunit 2, and outputs it. The processing is then completed.

The operation of the speech recognition unit 1 shown in FIG. 14 isdiscussed below with reference to the flow chart of FIG. 17.

Upon receiving input speech, in step S51, the speech recognition unit 1sets the forming unit of the speech recognition result corresponding tothe input speech. Immediately after a new speech is input, apredetermined default is set as the forming unit, in step S51.

In step S52, the speech recognition unit 1 recognizes the input speech.Then, in step S53, the speech recognition result obtained by using theforming unit which was set in step S51 is output to the machinetranslation unit 2. The process then proceeds to step S54 in which it isdetermined whether an alteration signal has been received from themachine translation unit 2 as the feedback information. If the outcomeof step S54 is yes, the process returns to step S51. In step S51, thepreviously set forming unit of the speech recognition result isincreased or decreased based on the alteration signal. Morespecifically, the forming unit may be changed from phrase to word(decreased), or conversely, from word to phrase (increased).Subsequently, the process proceeds to step S52, and the processingsimilar to the one discussed above is repeated. As a result, in stepS53, the speech recognition result with a smaller or greater formingunit, which was newly set based on the alteration signal, is output fromthe speech recognition unit 1.

If it is found in step S54 that an alteration signal as the feedbackinformation has not been received from the machine translation unit 2,the processing is completed.

The operation of the machine translation unit 2 shown in FIG. 15 is nowdiscussed with reference to the flow chart of FIG. 18.

Upon receiving text as a speech recognition result from the speechrecognition unit 1, in step S61, the machine translation unit 2 analyzesthe forming unit of the text. It is then determined in step S62 whetherthe forming unit is suitable for the processing to be executed in themachine translation unit 2.

The determination in step S62 may be made by analyzing the morphemes ofthe speech recognition result. Alternatively, the determination in stepS62 may be made as follows. Character strings forming the unit suitablefor the processing to be executed in the machine translation unit 2 maybe stored in advance, and the forming unit of the speech recognitionresult may be compared with the character strings.

On the other hand, if it is found in step S62 that the forming unit ofthe text is not appropriate for the processing to be executed in themachine translation unit 2, the process proceeds to step S63. In stepS63, an alteration signal for instructing the speech recognition unit 1to increase or decrease the forming unit to be a suitable one is outputto the speech recognition unit 1 as the feedback information. Then, themachine translation unit 2 waits for the supply of the speechrecognition result with an altered forming unit from the speechrecognition unit 1, and upon receiving it, the process returns to stepS61. Thereafter, processing similar to the aforementioned one isrepeated.

If it is found in step S62 that the forming unit of the text as thespeech recognition result from the speech recognition unit 1 isappropriate for the processing to be executed in the machine translationunit 2, the process proceeds to step S64 in which the speech recognitionresult is processed in the machine translation unit 2.

That is, the machine translation unit 2 translates the speechrecognition result, and outputs the translated result. Then, theprocessing is completed.

As discussed above, in response to an instruction from the machinetranslation unit 2, which performs natural language processing, thespeech recognition unit 1 alters the forming unit of the speechrecognition result to one suitable for the natural language processing,thereby enabling the machine translation unit 2 to easily performnatural language processing (translation) with high precision.

The dialog management unit 5 may also output the above-describedalteration signal to the speech recognition unit 1 as format informationso as to allow the speech recognition unit 1 to output the speechrecognition result with a unit suitable for the processing to beexecuted in the dialog management unit 5.

FIG. 19 illustrates a third example of the configuration of the speechrecognition unit 1. The same elements as those shown in FIG. 3 arerepresented by like reference numerals. Basically, the speechrecognition unit 1 shown in FIG. 19 is configured similarly to thatshown in FIG. 3, except that the provision of the adaptation processor19 is eliminated.

In the speech recognition unit 1 shown in FIG. 19, the matching portion15 is adapted to receive a request signal, which will be discussed indetail below, from the machine translation unit 2 as the feedbackinformation. Upon receiving a request signal, the speech recognitionunit 1 performs processing in accordance with the request signal. Inthis case, when the processed feature parameters are required, thematching portion 15 executes processing by the use of the featureparameters stored in the feature buffer 14, thereby obviating the needto request the user to re-issue the speech.

FIG. 20 illustrates a third example of the configuration of the machinetranslation unit 2 shown in FIG. 1 when the speech recognition unit 1 isconstructed such as the one shown in FIG. 19. The same elements as thoseshown in FIG. 4 are designated with like reference numerals. Basically,the machine translation unit 2 shown in FIG. 20 is configured similarlyto the counterpart shown in FIG. 4, except that a conversion-resultcorrecting portion 29 and a conversion result buffer 30 are provided.

In the machine translation unit 2 shown in FIG. 20, if the languageconverter 22 requires information necessary for performing highprecision processing while executing the processing, it outputs arequest signal, as the feedback information, for instructing thematching portion 15 of the speech recognition unit 1 shown in FIG. 19 tosend the information. Upon receiving the information from the matchingportion 15, the language converter 22 performs high precisionprocessing.

The conversion-result correcting portion 29 receives the languageinformation of the output language obtained from the language converter22 and evaluates it. If the evaluation result satisfies predeterminedcriteria, the conversion-result correcting portion 29 supplies thelanguage information from the language converter 22 to the textgenerator 23.

If the evaluation result of the language information does not satisfythe predetermined criteria, the conversion-result correcting portion 29temporarily stores the language information in the conversion resultbuffer 30, and also outputs a request signal, as the feedbackinformation, for requesting the matching portion 15 to send anotherpossible recognition result. Then, in response to the request signalfrom the conversion-result correcting portion 29, the speech recognitionunit 1 outputs another possible recognition result, which is thenprocessed in the text analyzer 21 and the language converter 22 and isfurther supplied to the conversion-result correcting portion 29 as thelanguage information of the output language. The conversion-resultcorrecting portion 29 then compares the newly received languageinformation with the language information stored in the conversionbuffer 30, and upon comparison, selects the more suitable one as thetranslation result of the input text and outputs it to the textgenerator 23.

FIG. 21 illustrates an example of the configuration of the languageconverter 22 and the language conversion database 26 shown in FIG. 20.

The language converter 22 is formed of the matching portion 51, whichconverts the language information of the input text supplied from thetext analyzer 21 to that of the output language by referring to thelanguage conversion database 26.

More specifically, the language conversion database 26 shown in FIG. 21is formed of a thesaurus dictionary 52 and a template table 53. Thethesaurus dictionary 52 stores, for example, as shown in FIG. 22, athesaurus in which words and the associated concepts (meanings) arehierarchically classified. In the example shown in FIG. 22, descriptionsin rectangles represent the concepts, while descriptions in ovalsindicate words. The numbers indicated in the rectangles areclassification numbers for specifying the concepts in the thesaurus.

Referring back to FIG. 21, the template table 53 registers templates inwhich Japanese sentence patterns are associated with those of Englishtranslations. In the templates, variables (X and Y in FIG. 21) are usedin some Japanese sentence patterns. The numbers added to the variablesrepresent the classification numbers in the thesaurus shown in FIG. 22.

In the language converter 22, the matching portion 51 selects thepattern of a Japanese sentence which is most similar (closest) to theinput text from the templates stored in the template table 53. That is,the matching portion 51 determines the distance between the input textand the pattern of the Japanese sentence of each template in thetemplate table 53, and then selects the template which contains thepattern closest to the input text. Further, the word corresponding tothe variable in the pattern of the Japanese sentence of the selectedtemplate is extracted from the input text, and the semantic distance(hereinafter sometimes referred to as “inter-word distance”) between theword and the concept to which the variable belongs is determined.

The inter-word distance between the variable of the selected templateand the corresponding word may be determined by the minimum numberrequired to shift from the node of the variable to the node of thecorresponding word (the number of branches forming the shortest pathfrom the variable node to the word node) in the thesaurus. If there is aplurality of variables in the selected template, the inter-word distancebetween each of the variables and the corresponding word is calculated.

The matching portion 51 selects the template and also finds theinter-word distance between the variable of the selected template andthe corresponding word, and then outputs the selected template, thecorresponding word, and the inter-word distance to the conversion-resultcorrecting portion 29. Simultaneously, the matching portion 51 outputsthe distance between the Japanese sentence pattern of the selectedtemplate and the input text (hereinafter sometimes referred to as“inter-pattern distance”) to the conversion-result correcting portion29. As discussed above, the inter-pattern distance is found when thetemplate closest to the input text is selected.

More specifically, for example, when the input text is “kanazuchi wotsukatta (A hammer was used)”, the template having the Japanese sentence“X (1.5621) wo tsukau (X (1.5621) is used)” is selected. Then, theselected template, the corresponding word “kanazuchi (hammer)”, theinter-pattern distance between the input text “kanazuchi wo tsukatta (Ahammer was used)” and the Japanese sentence “X (1.5621) wo tsukau (X(1.5621) is used)”, and the inter-word distance between the variable X(1.5621) and the corresponding word “kanazuchi (hammer)” are output tothe conversion-result correcting portion 29.

Basically, the matching portion 51 selects the template which makes theinter-pattern distance between the input text and the Japanese sentencethe shortest, as discussed above. However, it may be difficult todetermine the exact template since there may be two or more templateswhich are possibly selected. In this case, the matching portion 51outputs a request signal to request the speech recognition unit 1 tosend information required for determining the template, and uponreceiving the request signal, the matching portion 51 makes adetermination.

The operation of the machine translation unit 2 shown in FIG. 20 isdiscussed below with reference to the flow chart of FIG. 23.

A description is given below of the operation of the machine translationunit 2 shown in FIG. 20 with reference to the flow chart of FIG. 23.

In the machine translation unit 2, upon receiving input text from thespeech recognition unit 1 shown in FIG. 19 as a speech recognitionresult, in step S71, the storage content of the conversion result buffer30 is cleared. Then, in step S72, the text analyzer 21 analyzes theinput text and supplies the analysis result to the language converter22. In step S73, the language converter 22 selects the template, asdiscussed with reference to FIG. 21, and converts the languageinformation of the input text into that of the output text by using theselected template. The language converter 22 then outputs the selectedtemplate, the inter-pattern distance, the corresponding word, and theinter-word distance to the conversion-result correcting portion 29 asthe conversion result.

Subsequently, in step S74, the conversion-result correcting portion 29stores the language information (selected template, inter-patterndistance, corresponding word, and inter-word distance) of the outputtext in the conversion result buffer 30. It is then determined in stepS75 whether the inter-word distance supplied from the language converter22 is equal to or smaller than a predetermined reference value. If theoutcome of step S75 is yes, namely, if the semantic distance between theconcept to which the variable in the selected template belongs and thecorresponding word in the input text is small, it can be inferred thatthe corresponding word in the input text be a correct speech recognitionresult. Accordingly, the process proceeds to step S76 in which theconversion-result correcting portion 29 outputs the language informationof the output language stored in the conversion result buffer 30 in stepS74 to the text generator 23. Then, the text generator 23 generates textof the output language translated from the input text. The processing isthen completed.

In contrast, if it is found in step S75 that the inter-word distance isgreater than the predetermined reference value, namely, if the semanticdistance between the corresponding concept and the corresponding word ofthe input text is large, it can be inferred that the word of the inputtext is a wrong speech recognition result. In step S75, it is inferredthat the recognized word sounds the same as the correct input word, butis different in meaning. Then, the process proceeds to step S77 in whichthe conversion-result correcting portion 29 outputs a request signal forrequesting the speech recognition unit 1 shown in FIG. 19 to sendanother possible word, such as a homonym of the previously output word,to the speech recognition unit 1.

In response to this request signal, the speech recognition unit 1re-performs speech recognition processing by using the featureparameters stored in the feature buffer 14, and then, supplies a homonymof the previously output word to the machine translation unit 2 shown inFIG. 20. The speech recognition processing performed on homonyms may beexecuted by storing various homonyms in the dictionary database 17 ofthe speech recognition unit 1.

A homonym of the previous word is supplied from the speech recognitionunit 1 to the machine translation unit 2. Then, in step S78, the textanalyzer 21 and the language converter 22 perform processing on the newword substituted for the previous word (hereinafter sometimes referredto as “substituted text”). Then, the processed result is output to theconversion-result correcting portion 29.

If there is a plurality of homonyms of the previous word, they may besupplied from the speech recognition unit 1 to the machine translationunit 2. In this case, the machine translation unit 2 preparessubstituted text of each homonym.

Upon receiving the language information of the output language convertedfrom the substituted text from the language converter 22, in step S79,the conversion-result correcting portion 29 compares the receivedlanguage information with the language information stored in theconversion result buffer 30, and selects a more suitable one. That is,the conversion-result correcting portion 29 selects the languageinformation which contains the smallest inter-word distance (i.e., thelanguage information converted from the text having the wordsemantically closest to the concept to which the variable of theselected template belongs).

Then, the process proceeds to step S76 in which the conversion-resultcorrecting portion 29 outputs the selected language information to thetext generator 23, and the text generator 23 performs processing similarto the one discussed above. The processing is then completed.

If there are a plurality of substituted text, in step S79, among thelanguage information converted from the substituted text and thelanguage information stored in the conversion result buffer 30, thelanguage information having the smallest inter-word distance isselected.

The aforementioned processing is explained more specifically below. Itis now assumed, for example, that the input text is “kumo ga shiroi (Thespider is white)”, and the template having the Japanese sentence “X(1.4829) ga shiroi (X (1.4829) is white) is selected. The wordcorresponding to the variable X is “kumo (spider)”, and if the semanticdistance between the concept with the classification number 1.4829 andthe corresponding word “kumo (spider)” is large, the conversion-resultcorrecting portion 29 outputs the request signal described above to thespeech recognition unit 1 shown in FIG. 19 as the feedback information.Then, if the speech recognition unit 1 outputs another possible word,such as a homonym of the previous word, “kumo (cloud)”, to the machinetranslation unit 2 in response to the request signal, the machinetranslation unit 2 compares the two words and selects the word having asmaller semantic distance from the concept 1.4829.

Thus, even if the speech recognition unit 1 wrongly recognizes the inputspeech, in other words, even if a word which sounds the same as theactual word but is different in meaning is obtained (i.e., the wordwhich is acoustically correct but is semantically wrong), the wrongrecognition result can be corrected, thereby obtaining an accuratetranslation result.

The processing for selecting the template from the template table 53performed in the matching portion 51 shown in FIG. 21 is discussed belowwith reference to the flow chart of FIG. 24.

In step S81, a certain template is selected from the template table 53.Then, in step S82, the inter-pattern distance between the Japanesepattern described in the selected template and the input text iscalculated. It is then determined in step S83 whether the inter-patterndistance has been obtained for all the templates stored in the templatetable 53. If the result of step S83 is no, the process returns to stepS81 in which another template is selected, and the processing similar tothe aforementioned one is repeated.

If it is found in step S83 that the inter-pattern distance has beenobtained for all the templates stored in the template table 53, theprocess proceeds to step S84 in which the template having the smallestinter-pattern distance (hereinafter sometimes referred to as the “firsttemplate”) and the template having the second smallest inter-patterndistance (hereinafter sometimes referred to as the “second template”)are detected. Then, a determination is made as to whether the differencebetween the inter-pattern distance of the first template and that of thesecond template is equal to or smaller than a predetermined threshold.

If the outcome of step S84 is no, i.e., if the Japanese sentencedescribed in the first template is much closer to the input text thanthose of the other templates stored in the template table 53, theprocess proceeds to step S85 in which the first template is determined.The processing is then completed.

On the other hand, if it is found in step S84 that the difference of theinter-pattern distance is equal to or smaller than the predeterminedthreshold, that is, if the input text is similar to not only theJapanese sentence described in the first template, but also to thatdescribed in the second template, the process proceeds to step S86. Instep S86, the matching portion 51 sends a request signal, as thefeedback information, to request the speech recognition unit 1 shown inFIG. 19 to send an acoustic evaluation value for determining whichtemplate is closer to the input speech.

In this case, the speech recognition unit 1 is required to determine thelikelihood that the input text is the Japanese sentence described in thefirst template and the likelihood that the input text is the Japanesesentence described in the second template by using the featureparameters stored in the feature buffer 14. Then, the speech recognitionunit 1 outputs the likelihood values to the machine translation unit 2.

In the machine translation unit 2, the likelihood values of the firsttemplate and the second template are supplied to the matching portion 51of the language converter 22 via the text analyzer 21. In step S87, thematching portion 51 selects the template having a higher likelihoodvalue, and the processing is completed.

The aforementioned processing is explained more specifically below. Itis now assumed, for example, that the speech recognition result“kanazuchi wo tsukai (by using a hammer)” has been obtained, and theJapanese sentence “X (1.23) wo tsukau (X (1.23) is used)” and theJapanese sentence “X (1.23) wo tsukae (use X (1.23))” are determined tobe first template and the second template, respectively. In this case,if the difference between the inter-pattern distance of the firsttemplate and that of the second template is small, the likelihood valuesof the first template and the second template are determined. Then, inthe machine translation unit 2, the template having a higher likelihoodvalue is selected.

As a consequence, even if the speech recognition unit 1 wronglyrecognizes the input speech, a wrong recognition result can becorrected, thereby obtaining an accurate translation result.

The above-described processing executed in accordance with the flowchart of FIG. 24 may be performed on the third and subsequent templates.

In the processing executed in accordance with the flow chart of FIG. 23,a wrong recognition result is corrected by selecting a homonym which isclosest to the concept to which the variable in the selected templatebelongs. According to this processing, however, it is difficult to findsuch a homonym if there are a plurality of homonyms close to thecorresponding concept.

It is now assumed, for example, that as the homonyms of X (1.4830) inthe selected template “X (1.4839) de tabeta (ate it with X (1.4839)”,three homonyms “hashi (bridge)”, “hashi (edge)”, and “hashi(chopsticks)” are obtained. If the semantic distances between the threehomonyms and the corresponding concept are the same, it is verydifficult to determine the exact word.

To deal with such a case, the machine translation unit 2 shown in FIG.20 may send a request signal, as the feedback information, forrequesting the speech recognition unit 1 to determine the most probableword as the speech recognition result based on prosody, such as accentsand pitches, of the input speech.

For example, the above-described “hashi (bridge)”, “hashi (edge)”, and“hashi (chopsticks)” generally have the intonations shown in FIG. 25.Accordingly, the speech recognition unit 1 acquires the prosody of theinput speech based on the feature parameters stored in the featurebuffer 14, and detects which of the words “hashi (bridge)”, “hashi(edge)”, and “hashi (chopsticks)” appears to be closest to the prosody,thereby determining the most probable word as the speech recognitionresult.

A description is now given, with reference to the flow chart of FIG. 26,of the operation of the machine translation unit 2 shown in FIG. 20 whenoutputting the above-described request signal.

In the machine translation unit 2, processes similar to those in stepsS71 through S78 of FIG. 23 are executed in steps S91 through S98,respectively.

After the processing of step S98, the process proceeds to step S99. Instep S99, the conversion-result correcting portion 29 determines whetherthe inter-word distance of the language information of the outputlanguage converted from the substituted text is the same as that of thelanguage information stored in the conversion result buffer 30. If theresult of step S99 is no, the process proceeds to step S100 in which theconversion-result correcting portion 29 selects the language informationhaving the smallest inter-word distance, as in step S79 of FIG. 23.

The process then proceeds to step S96. In step S96, theconversion-result correcting portion 29 outputs the selected languageinformation to the text generator 23, which then forms text of theoutput language translated from the input text. The processing is thencompleted.

If it is found in step S99 that the inter-word distances of theabove-described two items of language information are equal to eachother, the process proceeds to step S101 in which the conversion-resultcorrecting portion 29 sends a request signal, as the feedbackinformation, for requesting the speech recognition unit 1 to determinethe most probable word as the speech recognition result based on theprosody of the input speech corresponding to the homonyms contained inthe substituted text and the input text.

In response to the request signal from the conversion-result correctingportion 29, the speech recognition unit 1 determines the most probableword (hereinafter sometimes referred to as the “maximum likelihoodword”) from the homonyms based on the prosody of the input speech, andsupplies it to the machine translation unit 2.

The maximum likelihood word is supplied to the conversion-resultcorrecting portion 29 via the text analyzer 21 and the languageconverter 22. Then, in step S102, the conversion-result correctingportion 29 selects the language information having the maximumlikelihood word, and the process proceeds to step S96. In step S96, theconversion-result correcting portion 29 outputs the selected languageinformation to the text generator 23, and the text generator 23generates text of the output language translated from the input text.The processing is then completed.

FIG. 27 illustrates a fourth example of the speech recognition unit 1shown in FIG. 1. The same elements as those shown in FIG. 3 aredesignated with like reference numerals. The speech recognition unit 1shown in FIG. 27 is configured similarly to the counterpart shown inFIG. 3, except that the adaptation processor 19 is eliminated and aspecific-field dictionary group 20 consisting of dictionaries sortedaccording to field are provided.

The specific-field dictionary group 20 is formed of N dictionariessorted according to field, and each dictionary is basically formedsimilarly to the word dictionary of the dictionary database 17, exceptthat it stores language models concerning words (phrases) for specifictopics and fields, that is, language models sorted according to task.

In the speech recognition unit 1 shown in FIG. 27, the matching portion15 executes processing by only referring to the acoustic database 16,the dictionary database 17, and the grammar database 18 under normalconditions. However, in response to a request signal from the machinetranslation unit 2, the matching portion 15 also refers to necessaryspecific dictionaries of the specific-field dictionary group 20 toexecute processing.

FIG. 28 illustrates a fourth example of the configuration of the machinetranslation unit 2 shown in FIG. 1 when the speech recognition unit 1 isconstructed such as the one shown in FIG. 27. The same elements as thoseshown in FIG. 20 are indicated by like reference numerals. The machinetranslation unit 2 shown in FIG. 28 is similarly configured to thatshown in FIG. 20, except that a field inference portion 61 is provided.

An analysis result of the input text from the text analyzer 21 and arequest signal from the conversion-result correcting portion 29 aresupplied to the field inference portion 61. Then, based on the analysisresult from the text analyzer 21, i.e., based on the analyses of thespeech recognition results of the previously input speech, the fieldinference portion 61 infers the task, such as the field or the topic, ofthe user's speech. Upon receiving a request signal from theconversion-result correcting portion 29, the field inference portion 61sends a request signal, as the feedback information, for requesting thespeech recognition unit 1 shown in FIG. 27 to execute processing byreferring to the specific dictionary corresponding to the designatedfield or topic.

Details of the method for inferring the field or the topic from inputspeech are discussed in, for example, Field inference method innatural-language search system, Katsuhito BESSHO, Naruhito IWASE, MiharuTOBE, and Yoshimi FUKUMURA, IEICE Trans., D-II J81-DII, No. 6 pp.1317-1327.

The operation of the machine translation unit 2 shown in FIG. 28 isdiscussed below with reference to the flow chart of FIG. 29.

In the machine translation unit 2 shown in FIG. 28, processes similar tothose of steps S71 through S74 of FIG. 23 are executed in steps S111through S114, respectively.

After the processing of step S114, the process proceeds to step S115 inwhich the conversion-result correcting portion 29 determines whether theinter-pattern distance supplied from the language converter 22 is equalto or smaller than a predetermined reference value. If the result ofstep S115 is yes, namely, if the speech recognition result is close tothe Japanese sentence described in the selected template, it can beinferred that a correct recognition result is obtained without the useof the specific-field dictionary group 20 of the speech recognition unit1 shown in FIG. 27. Then, the process proceeds to step S116 in which theconversion-result correcting portion 29 outputs the language informationof the output language stored in the conversion result buffer 30 in stepS114 to the text generator 23. The text generator 23 then forms text ofthe output language translated from the input text. The processing isthen completed.

Conversely, if it is found in step S115 that the inter-pattern distanceis greater than the predetermined reference value, namely, if the speechrecognition result is not close to the Japanese sentence described inthe selected template, it can be inferred that a correct recognitionresult cannot be obtained unless the specific-field dictionary group 20is used as well as the ordinary databases. Then, the process proceeds tostep S117 in which the conversion-result correcting portion 29 sends thefield inference portion 61 a request signal for requesting the executionof speech recognition processing with the use of the specific-fielddictionary group 20.

The field inference portion 61 infers the topic or field of the inputspeech by referring to the output of the text analyzer 21. Uponreceiving a request signal from the conversion-result correcting portion29, the field inference portion 61 supplies a request signal, as thefeedback information, for requesting the speech recognition unit 1 toexecute processing by referring to the specific dictionary associatedwith the inferred topic or field.

More specifically, if the field inference portion 61 infers that thetopic of the input speech is concerned with traveling, it sends arequest signal for requesting the speech recognition unit 1 to executeprocessing by referring to the specific dictionary for registering thenames of sightseeing spots.

In this case, by using the feature parameters stored in the featurebuffer 14, the speech recognition unit 1 performs speech recognitionprocessing by further referring to the specific dictionary forregistering the words (phrases) associated with the topic or field inaccordance with the request signal. That is, the vocabularies used forspeech recognition can be extended in performing speech recognitionprocessing. The speech recognition result obtained as discussed above isthen supplied to the machine translation unit 2 shown in FIG. 28.

Upon receiving the new recognition result, in step S118, in the machinetranslation unit 2, the text analyzer 21 and the language converter 22execute processing on the input text as the new recognition result, andthe processed result is output to the conversion-result correctingportion 29.

Upon receiving the language information of the output language from thelanguage converter 22, in step S119, the conversion-result correctingportion 29 compares the received language information with that storedin the conversion result buffer 30, and selects a more suitable one.More specifically, the conversion-result correcting portion 29 selectsthe language information having a smaller inter-pattern distance.

The process then proceeds to step S116 in which the conversion-resultcorrecting portion 29 outputs the selected language information to thetext generator 23. Thereafter, the text generator 23 performs processingsimilar to the one discussed above. The processing is then completed.

As discussed above, the machine translation unit 2 feeds back a requestsignal, as the feedback information, to the speech recognition unit 1according to a result of the processing which has been half done. Inresponse to this request signal, the speech recognition unit 1 performsappropriate processing accordingly. It is thus possible to performhigh-level natural language processing on the input speech.

That is, the speech recognition unit 1 performs relatively simple speechrecognition processing, and when a question arises or information isrequired in the machine translation unit 2 while processing the receivedrecognition result, the machine translation unit 2 requests the speechrecognition unit 1 to perform processing for solving the question or tosend the required information. As a result, high-level natural languageprocessing can be easily performed on the input speech in the machinetranslation unit 2.

In this case, it is not necessary to instruct the user to re-issue thespeech or to check with the user whether the speech recognition resultis correct.

Although in this embodiment the machine translation unit 2 conductstranslation by the use of the templates having the Japanese sentencepatterns, other types of templates, such as examples of usage, may beused.

The above-described processes may be executed by hardware or software.If software is used to execute the processes, the corresponding softwareprogram is installed into a computer which is built in a dedicatedspeech processing system, or into a general-purpose computer.

A description is given below, with reference to FIGS. 30A, 30B, and 30C,a recording medium for storing the program implementing theabove-described processes which is to be installed into a computer andexecuted by the computer.

The program may be stored, as illustrated in FIG. 30A, in a recordingmedium, such as a hard disk 102 or a semiconductor memory 103, which isbuilt in a computer 101.

Alternatively, the program may be stored (recorded), as shown in FIG.30B, temporarily or permanently in a recording medium, such as a floppydisk 111, a compact disc-read only memory (CD-ROM) 112, a magnetooptical (MO) disk 113, a digital versatile disc (DVD) 114, a magneticdisk 115, or a semiconductor memory 116. Such a recording medium can beprovided by so-called package software.

The program may also be transferred, as illustrated in FIG. 30C, to thecomputer 101 by radio from a download site 121 via a digital-broadcastartificial satellite 122, or may be transferred by cable to the computer101 via a network 131, such as a local area network (LAN) or theInternet, and may be then installed in the hard disk 102 built in thecomputer 101.

In this specification, it is not essential that the steps of the programimplementing the above-described processes be executed in time seriesaccording to the order indicated in the flow charts, and they may beprocessed individually or concurrently (parallel processing and objectprocessing may be performed to implement the above-described steps).

The program may be executed by a single computer, or a plurality ofcomputers may be used to perform distributed processing on the program.Alternatively, the program may be transferred to a distant computer andexecuted.

FIG. 31 illustrates an example of the configuration of the computer 101shown in FIG. 30. The computer 101 has a built-in central processingunit (CPU) 142. An input/output interface 145 is connected to the CPU142 via a bus 141. When an instruction is input from a user by operatingan input unit 147, such as a keyboard or a mouse, into the CPU 142 viathe input/output interface 145, the CPU 142 executes the program storedin a read only memory (ROM) 143, which corresponds to the semiconductormemory 103 shown in FIG. 30A. Alternatively, the CPU 142 loads thefollowing type of program into a random access memory (RAM) 144 andexecutes it: a program stored in the hard disk 102, a programtransferred from the satellite 122 or the network 131 to a communicationunit 148 and installed in the hard disk 102, or a program read from thefloppy disk 111, the CD-ROM 112, the MO disk 113, the DVD 114, or themagnetic disk 115 loaded in a drive 149 and installed in the hard disk102. Then, the CPU 142 outputs the processed result to a display unit146 formed of, for example, a liquid crystal display (LCD), via theinput/output interface 145.

1. A speech processing system comprising: a speech recognition unitconfigured to receive and perform speech recognition on input speech toproduce a speech recognition result using acoustic models; and anatural-language processor configured to perform natural languageprocessing on said speech recognition result, said natural-languageprocessor including: a speech zone detector configured to detect correctzones from said speech recognition result; a feedback unit configured tofeed back information obtained as a result of the natural languageprocessing performed on said speech recognition result to said speechrecognition unit, the feedback information including said detectedcorrect zones, wherein said speech recognition unit includes anadaptation processor to process the feedback information from saidfeedback unit to adapt said acoustic models so that said speechrecognition unit produces the speech recognition result with higherprecision than when said adaptation processor is not used.